Xerography



Oct. 11, 1960 F. A. STEINHILPER Filed Aug. 1, 1955 21- NEGATIVE HIGHVOLTAGE SOURCE 17 2 25 12 9 16 i zs C POSITIVE HIGH VOLTAGE 22 SOURCEZZ\ POSITIVE HIGH VOLTAGE SOURCE NEGAT|VE HIGH VOLTAGE 50 U RC E 2Sheets-Sheet 1 mzzzzmd INVENTOR. FRANK A. STEINHILPER Arrmr Oct. 11,1960 F. A. STEINHILPER 2,955,938

XEROGRAPHY Filed Aug. 1, 1955 2 Sheets-Sheet 2 NEGATIVE f2] POSITIVENEGATIVE -21 POSITIVE HIGH VOLTAGE 2 HIGH VOLTAGE HIGH VOLTAGE 22 HIGHVOLTAGE SOURCE SOURCE SOURCE SOURCE L 1/ 10 3a +Hux++++ WWW J l .L 5'7.i. 37

N EGATIVE HIGH VOLTAGE SOU RC E \5;

66, POSITIVE HIGH VOLTAGE SOURCE A NEGKAST'LVE POSITIVE HIGHVOLTAGE T GE0 wz becz SOURCE -75 FIXING STATION POWDER C LOUD \9/ GENERATOR y- 9INVENTOR.

FRANK A. STEINHILPER ATTORNEY United States 2,955,935 XEROGR'APHY FrankA. Steinhilper, Rochester, N.Y., assignor to Haloid Xerox'Inc acorporation of New York Filed Aug. 1', i955, Ser. N6. 35,496- 6 Claims.(11, 96-'-1) This invention relates to xerogr'aphy. M in terography, itis usual to form an electrostatic charge pattern on the surface of aXerographic plate composed of a photoconductive insulating layer on aconductive backing member. The pattern is formed by first sensitizingthe plate by placing an electrostatic charge on the surface of thephotoconductive insulating layer.- While in a serisitized condition, theplateis exposed to anactivating radiationpattern such as a light imageor the like. The activating energy such as light causes dissipation ofcharge whereas areas not affected by exposure, i.e.- areas for egran plenot struck by light remain in their charged condition Thus, afterexposure to a pattern of activating riadialtioman electrostatic image ofelectrostatic charges I e itists on the surface of the xerographicplate; This pattern inay be developed or otherwise utilized; Ifdeveleped, usual grerographic development techniques such as eascade orpowder cloud development may be used to make the electrostatic imagepattern visible. A developed imageon the plate surface may be viewed,photographed or the like or may be transferred to a transfer base whereit may be permanently afiix'ed.

Charging to about 100 to 800 volts or sensitization of thephotoconductive insulating layer ofthe xerographic plate, is generallyaccomplished through the deposition ions created by a corona dischargeelectrode moving at a uniform rate above the plate surface.- The ionsdeposit due to the electrostatic fields of force; which exist betweenthe corona electrode and the backing member of theplate which is held ata grounded potential;

It has nowbeen found that the art of xerography may be extended throughthe use of a photoconductive insulating layer which is not on aconductive support base, Speeiiically, iterography carried out in thisinvention using plates comprising photoconductive insulating layers oninsulating support bases and also self supporting films ofphotoconductive insulating material. It is therefore an object of thisinventionto devise a xa-agtaphic plate comprising a photoconductiveinsulating layer on an insulating support base;

It is a further object of this invention to devise n'ovel methods ofapplying auniform electrostatic field through a photoconductiveinsulating layer.

is a still further object of this invention to'devise novel methods ofsensitizing a self-supporting film "of photoconductive insulatingmaterial;

It is yet another object of this invention to devise novel methods ofsensitizing a photoconductive insulating layer backed by an insulatinglayer. a

It is another object of this invention to devise novel methods of imageformation in the art of nerography. I

It is a further object of this invention to devise methods ofxro'g'raphy image formation on a Xerograpliic plate comprising aphotocon'ductive insulating layer hot Bagged by a conductive backinglayer.

elt is a still further objectof this invention -to devise hovel methodsof xei'dgra'plii'c image formation on the Patent C) "ice Patented- Oct;11-, 1960 2. surface of a photo'conductive' insulating layer on aninsulating support base. I

It is a further object of this invention to" devise new means andapparatus in the art of xerography.

It is still further an object of this invention to devise an automaticxerographic machine using a plate" nre'mb'er comprising aphoto'conductive insulating layer on an insula'ting support base.

In the drawing:

Fig. 1 is a transverse sectional view of an embodiment of a xerographicplate comprising a photoconductive insulating layer supported ori aninsulating support base;

Fig. 2' is a transverse sectional view of an embodiment of a xerographicplate comprising a self-supporting film of photoconductive insulatingmaterial;

Fig. 3 is a diagrammatic representation of anernbodiment of a firstcharging step of the xerographic plate illustrated in Fig. -1;

Fig. 4 is a diagrammatic representation of an embodiment of the secondcharging step following charging as illustrated in Fig. 3 to create asensitive plate;

Fig. 5 illustrates exposure of a sensitive plate;

Fig. 6 is a flow step illustrating development of an electrostati'eimage b'earin'g plate;

Fig: 7 is a diagrammatic illustration of another embodiment of the firstcharging step of either the plate illustrated in Fig; 1 or the plateillustrated in Fig. 2; Fig. 8 is a diagrammatic illustration of anotherembodiment of the second charging step following charging as illustratedin Fig. 7 resulting in a sensitive plate ac;- cording to this invention;

Fig. 9 is an embodiment of an automatic machine according to thisinvention;

For a better understanding of this invention, together with otherfurther objects thereof, reference is now had to the followingdescription taken in connection with the accompanying drawings, and thescope of the invention will be pointed out in the appended claiins.

Referring now to the drawings, in Figure 1 there is innstrated oneembodiment of a plate to' which this invention is directed; The plate iscomposed of a photocoiiducftive insulating layer 12, overlying a supportmember 11 of iiisulating material: The photocoriductive insulating layer12 may be any of a number of materials, as for example, amorphous orvitreous selenium, anthracene, sulphur, tellurium, various mixtures ofthese materials or photooiiductive insulating materials in insulatingbinders as for examplezine oxide in a resin binder. Otherphotoconduetive insulating materials include, but are in no way limitedto, zinc=magnesiuni oxide, zinc sulfide, zinc cadrnium sulfide, cadmiumsulfide, cadmium strontium suifide, zinc silicate, calcium tungstate,slenides an'd iiiiied selepides of cadmium and zinc, anthracene,titanium di-'- oxide, and the like. These materials are, in someiiistances, coated directly on the surface and in other instances theyare coated in a resin binder on the surface of the material. Desirably,they are activated with small amounts, that is 001% to '0;001% ofmetallic impurities, as is well known to those skilled in the art. I

I The base member 11 is composed of insulating mate'- rial whether rigidor flitible and desirably comprises a layer of equal thicknessthroughout having smooth surfaces. Materials which may be used are mica,plastics, glass, rubber, insulating cloth materials and other insalating materials generally known to the art. Photocom ductive insulatinglayer 12 may be placed on insii "ting support member 11, usingconventional coating techniques such as dipping, spray coating,evaporation, casting or the lilge.

In Fig; 2 there is illustrated a plate comprising a selfsupporting filmof photoconductive insulating material 10. The photoconductive materialmay comprise any of the various material described in connection withFig. 1. These materials are in some instances prepared immediately as aself-supporting film, whereas in other instances they are coated on asurface and then stripped from the surface. One which is presentlypreferred has been made using the stripping technique by forming a layerof zinc oxide in a resin binder on a polyethylene coated surface andthen stripping it therefrom. Desirably, the self-supporting film isuniform in thickness throughout and has smooth surfaces.

In Fig. 3 there is illustrated an embodiment of the first step of platesensitization according to this invention. The plate composed ofphotoconductive insulating layer 12 overlying insulating backing member11, is passed between corona electrodes 13 and 15 in a direction asillustrated by the arrow. Positioned in close proximity to coronaelectrode 13 are lamps 23. The lamps 23 are illuminated during charging.Although in this embodiment lamps are illustrated, any form of uniformradiation may be used as for example a beta source or the like and suchmodifications are intended to be included herein. Corona electrode 13comprises corona discharge Wire or wires 16 surrounded by shield 17 heldat a ground potential. The corona discharge wire or wires 16 are biasedto a negative high voltage which is supplied from negative high voltagesource 21. Corona discharge electrode 15 comprises shield 20 held atground potential and corona discharge wire or wires 18. Corona dischargeelectrode 15 is biased to a positive high voltage which is supplied frompositive high voltage source 22 to corona discharge wire or wires 18.The positive high voltage on corona wire or wires 18 of corona electrode15 supplies positive ions to the exposed surface of support member 11whereas the negative potential applied to the discharge wire or wires 16of corona electrode 13 creates negative ions for deposition on thephotoconductive insulating layer 12. Since the photoconductiveinsulating layer is illuminated by lamps 23, this layer is conductiveand thus the negative ions which reach the surface of photoconductiveinsulating layer 12 are drawn through the layer to the interlayer areabetween photoconductive insulating layer 12 and insulating supportmember 11. The negative charges 26 deposit at the interlayer area, it isbelieved, due to electrostatic fields created by the combined effect ofthe positive ions sprayed by corona electrode 15, some of which depositas positive charges 25 on the surfaces of insulating support member 11,and the positively biased corona electrode 15.

In Fig. 4 there is illustrated an embodiment of the next step insensitizing a photoconductive layer when such a layer is supported on aninsulating base. In this figure as in Fig. 3, the plate composed ofphotoconductive insulating layer 12 overlying insulating support base 11is again passed between corona electrodes 13 and 15. As in the previousfigure corona electrode 13 comprises a grounded shield 17 and a coronadischarge wire or corona discharge wires 16 and corona dischargeelectrode 15 comprises a grounded shield 20 and a corona discharge wireor corona discharge wires 18. Corona discharge wire or wires 16 ofcorona electrode 13 are now connected to the positive voltage source 22and thus spray positive ions whereas corona discharge wire or wires 18of corona electrode 15 are now connected to the negative high voltagesource 21 and thus corona discharge electrode 15 sprays negative ions.The plate is being moved in this figure from left to right as isillustrated by the arrow and thus the left portion of the plate has notas yet passed between corona discharge electrodes 13 and 15. Thoseportions of the plate not yet exposed to the charging mechanism carrynegative charges 26 at the interlayer area and positive charges 25 onthe exposed side of the insulating support member 11. Negative charges26 and positive charges 25 were deposited during the charging operationdiscussed in connection with Fig. 3. Those portions of the plate exposedto the charging mechanism of this figure carry positive charges 27 fromthe positive sprayed corona discharge electrode 13 on the upper surfaceof the photoconductive insulating layer 12 whereas the charges on theexposed or lower surface of the insulating support base 11 areneutralized by the negative spraying corona discharge electrode 15 whichdeposits negative charges in an amount equal to the positive chargeswhich were deposited during the operation illustrated in Fig. 3, and thenegative and positive charges 28 on the exposed or lower surface of theinsulating support member 11 combine and neutralize each other. Thus,there is created, following the two charging operations shown in Figs. 3and 4, a layer of charge 26 at the interlayer area and a layer of charge27 on the exposed surface of the photoconductive insulating layer 12. Anelectrostatic field exists between charges 26 and charges 27. This fieldwould normally draw the charges to one another. However, charges remainbound in place due to the insulating characteristics of photoconductiveinsulating layer 12 while the layer is kept in darkness.

In Fig. 5 there is illustrated exposure of a sensitized xerographicplate composed of a photoconductive insulating layer 12 overlying aninsulating support base 11. However, it is to be realized that the plateused during exposure in this figure is for illustrative purposes onlyand that the self-supporting film of photoconductive insulating materialmay be used as well. Just prior to exposure a layer of charge 26 existsat the interface between the photoconductive insulating layer 12 andsupport base 11 and a layer of charge 27 exists throughout the topturface of photoconductive insulating layer 12. During exposure, areasof photoconductive insulating layer 12 struck by light, becomeconductive and in those areas the bound charges of charged layer 27 andof charged layer 26 becomes unbound and migrate toward one another tobecome neutralized or dissipated resulting in discharged areas 33. Thereis illustrated in this figure the projection of the light pattern ofcopy 36* which is illuminated by lamps 31. The light pattern isprojected through lens 32 to the surface of photoconductive insulatinglayer 12. It is to be realized that although projection exposure isillustrated in this figure there is no intent to be limited thereto,instead it is intended that the various means of exposure known to thosein the art as for example contact exposure or the like may be used andare intended to be included herein. It is also to be realized thatalthough exposure only to a light pattern is shown, there is intended tobe included herein exposure to all forms of activating radiation as forexample X-rays or the like.

The time of exposure will depend on various factors such as theintensity of the lamps, whether contact exposure or projection exposureis being used, the potential of charge on the xerographic plate, thespeed of the photoconductive insulating layer 12, and the like.Depending on the various combinations of elements used, exposure mayvary from a fraction of a second to many minutes and there is no intentin this application to be limited to any particular time of exposure.

It is also to be realized that when the backing member or the supportlayer is transparent, exposure may be made through the backing memberinstead of directly to photoconductive insulating layer 12. It is alsoto be realized that depending on the particular material andcharacteristics of photoconductive insulating layer 12, if the backingmember is transparent reflex exposure is also possible and is intendedto be included herein.

Reference is now had to Fig. 6 wherein is illustrated one technique ofdevelopment of charged patterns. The xerographic plate being developedis composed of a photoconductive insulating layer 12 overlying aninsulating backing support 11. However, it is to be realized that theparticular plate is included for illustrative purposes only anddevelopment may be carried out in a similar fashion with self-supportingfilms of photoconductive instrains material; The technique of sevens Ytrated ....fi re is en a ly owain. 495, as cad s' s'l em: vT s. o m a vop iit nd ya us developing materials are described in Wise U.S. ifat n'tasis s sz Walkup and Wise s. Patent 2';6'38;41 6,' Walkup Us. Patent2,618,551 and various 9 er 'atents'. I Cascade type of developercomprises finerp'articlesadhering, due to electrostatic attraction, toer-awe... a In this' figure there is illustrated a developing tray 35 wh a plateagainst the bottom thereof. The developer illustrated-ascascading across the surface of the which carries the electrostaticcharge pattern and ge development takes place through depositing of thefin Y particles on the charged area of photoconductive insul ing layer12. Generally it is desirable whenusing e development to cascade theparticles back and across the surface a few times to assure dense deaSince areas as yet undeveloped which carry are sensitive' to light, itis desirable to carry out pnient in the dark. This may he accomplishedin tray sirnilar-to tray 35 by placing a shield or dark v acrossthe openarea of the tray following positioning of the plate in darkness againstthe base thereof. Other means that keep the plate in darkness areintended to be included herein. v V r k p h Although cascade developmentof the image is ilrustrated there is no intent to be limited theretoinsteadit is intended that the various means of development known ifthose in the art maybe used. For example, a techniknown aspowderclouddeveloprnent is describ ed in pa 2,221,776 and could be usedto develop charge p t rnsforrned according to this invention. It is alsoto realized that development techniques otherthan those illustratedwhich are known to those in the are also intended. to be included hereinas for example magnetic development or the like. p

n Figs. 7 and 8 there is, illustrated anotherembodiinent ofsensitization of a plate according to this inventicn. In these figures aplate comprising a self-supporting filrn' of photoconductive insulatingmaterial 10 is positioncd on a conductive grounded electrode 37., Acorona electrode comprising a grounded conductive shield 42 and a coronawire or wires 43 is positioned over the plate surface and theplate ismoved in the direction of .the arrow. the first charging pass as isillustrated in Fig. 7 alanip 40 .is illuminated thus making thephotoconducinsulating layer 10 conductive. In Fig, 7 switch 41 cdrinectscorona discharge wireor wires 43 of corona discharge electrode 44 topositive high voltage source 22 a thus there is deposited positivecharges 38 at the lower surface of photoconductive insulating layer 10.Ihe negative high voltage source-21 may be connected thropgh switch 4lto the corona discharge wire or wires but is not -soconnected in Fig. 7.Following positive electrostatic charging of the plate switch 41 isthrown to position illustrated in Fig. 8 negative highvoltage is sprayedfrom corona discharge electrode 44 supplied with negative high voltageto corona discharge wire or ires43 of the discharge electrode fromsource 21 through 41. Thus, in the second pass of the electrode over thesurface, there is sprayed negative corona to the surface of thephotoconductive insulating layer 16 positioned on conductive groundedelectrode 37. The plate in Fig. 8 is moved, in the direction indicatedby the arrow and the shield 42 is again grounded. Following passage ofcorona discharge electrode 44 as indicated in Figs. 7 and 8 there isdeposited a layer of negative charge 45 on the uppersurfaceofphotoconductive insulating layer 10 and a layer of positive charge 38atthe lower surface of photoconductive insulating layer l0. There isthus created a sensitive xerographic plate which is ready forexposureand then development as discussed in connection with lfl' andfi- .7.

Optionally, and in accordance with this invention devloprnent of theimage maybe or ni tted andin 4 electrostatic charge pattern may beusedfor irn g fo altion as" for example by scanning; transfer; or thelike" as is well known the art. c i H H I j v Although the plate used inFigs. 7 and 8 co self-supporting film of photoco'n'ductiye n 1 I rial,it is to be realized that the particular platehasl been used forillustrative purposes only. plate illustrated in Fig. 1 comprising aphotoconductive' insulating la r on an insulating layer may also usediwhenchargl is carried out as is illustratedin fig. 7 using a platej co jprising a photoconductive insulating layer on an insu'l support base thepositive charges sprayed to: the p e will deposit at the interface ofthe photoconductivellnsulating layer and the insulating 'support base.charge is sprayed as illustrated in Fig; 8, negative charges willdeposit on the surface of the photoconductiveinsulat: ing layerresultingin a charge sensitive xerographic plate similar to the chargedplate created renewing charging in When using the plate illustratedinFigs, 7 andfi charg ing in Fig. 7 results charge deposition at the ldwersurface of the self-supporting film 10. The charges rernain in positionon the plate and not travel to electrode 37 y due to a minute air gapwhich will separate ute o from electrode 37 when these elements are innormal surface contact. This air gap provides a suflici tinsulating.dielectric layer-to prevent charge; transfer dissipation. By preventingcharge movement to' the el trode, the air gap .or other gas gap aidscreating the surface charge desired at the lower sjurface which br ngsabout the surface chargedesired on the upper surface creating the fieldsof force necessary to cause charge deposition as is illustratedinFigg 8.Reference is now had to Fig.2 w'li thereis' sho'wn an embodiment of anautomatic rriaclnrie according to this invention. A drum 50 driven atits sassy rnctc 52 57 negative high voltage is supplied to baron -as" gewires 62 of corona discharge electrode by neg high voltage source 63,and positive highv'ol ge. supplied to corona discharge wires 65o]?corona electrode 60 hy positive hig voltage source '66. the previousembodiments, the shields 67 and 68 held at ground potential At thesecond charging station, gen} erally designated 70, positiveliighvoltage is supplied ,tig corna discharge wires 71 of corona dischargeelectrode 72 from positive high voltage source "73, and negative highvoltage is supplied to corona discharge of corona discharge electrode 76from negative high voltage, sdiirefe 77. Shield 78' of corona dischargeel'cltjrc d 7min shield 80 of corona discharge electrode 72 are held atground potential. Following chargiiig at stations 57' a d spool throughthe of pro'e'aibhana then yv ind up spool 86; The wind-" ip; spool is byGr 87 h g shbs 8 Mo s l ti is f0 ,7 a synchronizing pace with he speedat o atlng drum 511. Various other news tclmique's or existing as; is a7 moving drum may be used and are intended to be included Within thescope of this invention.

Following exposure, the drum is next rotated to development station 90.In this embodiment a powder cloud generator 91 generates an aerosol ofxerographic developer particles and passes the aerosol through conduit92 to the surface of the photoconductive insulating layer 55 to bedeveloped. Also there is diagrammatically shown in this figure adevelopment electrode 93 and development takes place as is well known inthe art on the surface of the photoconductive image bearing layerbeneath development electrode 93. Next in the path of movement of therotating drum 50 is a transfer station 95. Various techniques oftransferring a developed electrostatic image may be used, as forexample, electrostatic transfer or the like, transfer to single sheetsor the like, and the like. In this embodiment there is illus trated whathas generally become known as adhesive transfer. A supply spool 96provides a web of material 97 carrying an adhesive coating on onesurface thereof. The adhesive coating is pressed against the surface ofthe photoconductive insulating layer 55 by a pressure roller 98 and theweb 97 is then fed through a fixing station 100 wherein the image on thesurface of web 97 is made permanent as, for example, through heatfusing, vapor fusing, by applying a protective coating, or the like. Theweb 97 may be cut up following fixing into individual copies or printsor, as illustrated, may be Wound up on take-up spool 101. A motor 104 isillustrated in this figure as driving take-up spool 101 through belt105. The movement of web 97 is synchronized with the movement of drum 50and optionally may be driven by motor 52 which may also be used to drivecopy 82. Drum 50 is next fed to a cleaning station generally designated102 whereat a rotating brush 103 wipes clean the surface of thephotoconductive insulating layer. The material removed from the surfacemay be drawn away from the surface with vacuum cleaning means or thelike. Fol lowing cleaning, drum 50 is ready for re-cycling through thevarious stations or stages described.

Although the charging grid described throughout has been of the sametype, it is to be realized that there is no intention to limit thisinvention thereto. For example, the corona discharge device may be ofthe type described in Walkup application Serial No. 154,295, filed April6, 1950, for Charging Device. This comprises a grid of fine wires whichis held at several thousand volts potential with respect to a groundedshield similar to the one shown and a control grid of coarser wires thanthe discharge wires located between the corona discharge wires and thesurface to be charged. The grid of coarser wires is held at anintermediate potential of several hundred volts above ground potentialand serves to control or limit the potential placed upon the surfacebeing charged. Also, there may be used stationary corona charging gridsas is known to the art, or radioactive charging means, or the like.

The high voltage power supply may comprise known circuits such as atransformer-rectifier circuit and a voltage dividing resistance forsupplying the required potentials, or the like.

The potential supplied to the corona discharge wires should be in theorder of several thousand volts as, for example, 6,000 to 8,000 volts.Although there is no intent to limit this invention to any particulartheory of operation, it is presently believed that, when a layer ofcharge exists at the interface between the photoconductive insulatinglayer and the insulating support base when using plates comprisingphotoconductive layers overlying an insulating support base or when alayer of charge exists at the lower surface of the photoconductor whenusing self-supporting films, and an opposite charge exists on the outersurface of the photoconductive insulating layer, complete discharge ofcharges in areas exposed to light takes place. Development of such acharge pat- '8 tern results in copy having high contrast and very littlebackground.

Following charging, as illustrated in Figs. 3 and 4, the potential onthe uncoated surface of the insulating base ll is substantiallyneutralized and thus the plate may be positioned on substantially anysurface as, for example, a ground metallic conductor, a table top, orthe like. Similarly, in connection with the embodiment illustrated inFigs. 7 and 8 if a photoconductor supported on an insulator is beingused substantially no potential is found on the uncoated surface of thesupport base; thus, no problems are encountered during exposure orsubsequent development whether the surface of the support base is or isnot in contact with a grounded or conduo tive electrode. If a slightpotential exists on the rear or uncoated surface of the support base,the potential would tend to increase as the support base is separatedfrom the grounded conductor 37. A point in separation would likely bereached, in such an instance, at which the po.- tential would becomesufficient to bring about a form of air breakdown and transfer of chargeto the surface of the support base. However, breakdown if it takes placewould be substantially uniform and charges transferred would not distortimage formation or a formed image on the photoconductive insulatinglayer.

When dealing with the self-supporting film of photoconductive insulatingmaterial of Fig. 2, it is to be realized that charging as illustrated inFig. 3 results in discharge of the charge through the illuminated andthus conductive photoconductive layer. Also, it is to be realized, thata charged and sensitive plate comprising a selfsupporting film ofphotoconductive material according to this invention carries a surfacecharge on the bottom and top surfaces. Since it is desirable to maintainthe charge through to exposure and since it is desirable to form thecharge pattern during exposure and maintain the formed pattern fordevelopment without distortion by stray charge deposition, it ispreferred that the steps of exposure and development are carried outwhen using a self-supporting film of photoconductive insulating materialwithout contacting the plate to an electrode. This may be accomplishedkeeping the plate in air during the various steps of image formation, bypositioning the plate on an insulating support surface, or the like.

The use of the term ground throughout this application is intended tohave the usual conventional meaning of a relative reference point. Thereis no desire for ground to limit this invention in any way to a specificvalue such as zero potential although in some instances ground mayindicate zero potential. Instead, ground is intended to indicate areference point from which other potential values vary upward whenpositive or downward when negative.

While the present invention as to its objects and advantages, as hasbeen described herein, has been carried out in specific embodimentsthereof, it is not desired to be limited thereby, but is intended tocover the invention broadly Within the spirit and scope of the appendedclaims.

What is claimed is:

1. The method of sensitizing a xerographic plate comprising a selfsupporting film of photoconductive insulating material prior to exposureand image formation in xerography, said method comprising applying afirst polarity corona generated electrostatic charge to a first surfaceof the photoconductive insulating film while said photoconductiveinsulating layer is uniformly illuminated by radiation which causes saidfilm to become electrically conductive and while an electric field isapplied through said film in a direction to move electrostatic chargedirected to said first surface to the opposite and second surface ofsaid photoconductive insulating film, said charge moved to said secondsurface being maintained at said second surface through the absence ofany electrode in electrical contact therewith, and then in the absenceof illumination of said photoconductive insulating film applying asecond and opposite polarity corona generated electrostatic charge tosaid first surface of said photoconductive insulating film forming asensitive xerographic plate with said first polarity charge at saidsecond surface and said second polarity charge at said first surface ofsaid photoconductive insulating film.

2. The method of sensitizing a xerographic plate comprising a layer ofphotoconductive insulating material overlying an insulating supportmember prior to exposure and image formation in xerography, said methodcomprising applying a first polarity corona generated electrostaticcharge to the outer and first surface of the photoconductive insulatinglayer of said Xerographic plate while said photoconductive insulatinglayer is uniformly illuminated by radiation which causes said layer tobecome electrically conductive and while an electric field is appliedthrough said plate in a direction to move electrostatic charge directedto said first surface to the opposite and second surface of saidphotoconductive insulating layer in contact with the insulating member,said charge moved to said second surface being maintained at said secondsurface through the absence of any electrode in electrical contacttherewith, and then in the absence of illumination of saidphotoconductive insulating layer applying a second and opposite polaritycorona generated electrostatic charge to said first and outer surface ofsaid photoconductive insulating layer forming a sensitive xerographicplate with said first polarity charge at said second surface and saidsecond polarity charge at said first surface of said photoconductiveinsulating layer.

3. The method of image formation in xerography in which a developableelectrostatic charge pattern is formed on the surface of a xerographicplate comprising a self supporting film of photoconductive insulatingmaterial, said method comprising applying a first polarity coronagenerated electrostatic charge to a first surface of a photoconductiveinsulating film while said photoconductive insulating film is uniformlyilluminated by radiation which causes said film to become electricallyconductive and while an electrostatic field is applied through said filmin a direction to move electrostatic charge directed to said firstsurface to the opposite and second surface of said photoconductiveinsulating film, said charge moved to said second surface beingmaintained at said second surface through the absence of any electrodein electrical contact therewith, then in the absence of illumination ofsaid photoconductive insulating film applying a second and oppositepolarity corona generated electrostatic charge to said first surface ofsaid photoconductive insulating film forming a sensitive xerographicplate with said first polarity charge at said second surface and saidsecond polarity charge at said first surface of said photoconductiveinsulating film, and exposing said sensitive xerographic plate to animage pattern of information to be recorded.

4. The method of claim 3 in which said developable electrostatic chargepattern formed on said Xerographic plate is developed with electroscopicmarking material forming a visible pattern of the recorded information.

5. The method of image formation in xerography in which a developableelectrostatic charge pattern is formed on the surface of a xerographicplate comprising a layer of photoconductive insulating materialoverlying an insulating support member, said method comprising applyinga first polarity corona generated electrostatic charge to the outer andfirst surface of the photoconductive insulating layer of saidxerographic plate while said photoconductive insulating layer isuniformly illuminated by radiation which causes said film to becomeelectrically conductive and while an electric field is applied throughsaid plate in a direction to move electrostatic charge directed to saidfirst surface to the opposite and second surface of said photoconductiveinsulating layer in contact with the insulating member, said chargemoved to said second surface being maintained at said second surfacethrough the absence of any electrode in electrical contact therewith,then in the absence of illumination of said photoconductive insulatinglayer applying a second and opposite polarity corona generatedelectrostatic charge to said first and outer surface of saidphotoconductive insulating layer forming a sensitive xerographic platewith said first polarity charge at said second surface and said secondpolarity charge at said first surface of said photoconductive insulatinglayer, and exposing said sensitive xerographic plate to an image patternof information to be recorded.

6. The method of claim 5 in which said developable electrostatic chargepattern formed on said xerographic plate is developed with electroscopicmarking material forming a visible pattern of the recorded information.

References Cited in the file of this patent UNITED STATES PATENTS2,277,013 Carlson Mar. 11, 1942 2,297,691 Carlson Oct. 6, 1942 2,543,051Oughton et al. Feb. 27, 1951 2,573,881 Walkup et al. Nov. 6, 19512,588,699 Carlson Mar. 11, 1952 2,624,652 Carlson Jan. 6, 1953 2,663,636Middleton Dec. 22, 1953 2,693,416 Butterfield Nov. 2, 1954 2,703,280Butterfield et al. Mar. 1, 1955 2,730,023 Greig Jan. 10, 1956 2,777,745McNaney Jan. 15, 1957 2,825,814 Walkup Mar. 4, 1958 2,833,648 Walkup May6, 1.958 2,833,930 Walkup May 6, 1958 OTHER REFERENCES Young et al.: RCAReview, vol. XV, No. 4, pages 469-484 (1954).

1. THE METHOD OF SENSITIZING A XEROGRAPHIC PLATE COMPRISING A SELFSUPPORTING FILM OF POTOCONDUCTIVE INSULATING MATERIAL PRIOR TO EXPOSUREAND IMAGE FORMATION IN XEROGRAPHY, SAID METHOD COMPRISING APPLYING AFIRST POLARITY CORONA GENERATED ELASTROSTATIC CHARGE TO A FIRST SURFACEOF THE PHOTOCONDUCTIVE INSULATING FILM WHILE SAID PHOTOCONDUCTIVEINSULATING LAYER IS UNIFORMLY ILLUMINATED BY RADIATION WHICH CAUSES SAIDFILM TO BECOME ELECTRICALLY CONDUCTIVE AND WHILE AN ELECTRIC FIELD ISAPPLIED THROUGH SAID FILM IN A DIRECTION TO MOVE ELECTROSTATIC CHARGEDIRECTED TO SAID FIRST SURFACE TO THE OPPOSITE AND SECOND SURFACE OFSAID PHOTOCONDUCTIVE INSULATING FILM SAID